As increasingly higher density connections are needed for circuit boards which have extremely high component packing density, the requirements for the connectors have become more and more severe and harder to meet. Especially after the circuit board has been completed with all of the components in place, the placement of the connector has become a critical feature in the method of circuit board fabrication.
The connector which must thereafter be connected has to have its electrical contacts connected to each of a number of circuit board leads or printed circuit pads. Thereafter, each pad is reflow soldered so as to assure great reliability for all the components on the boards and the board itself.
Because of the high packing density, the leads on a circuit board must be placed around the periphery thereof, and especially along one of the edges so that the component packing density may further be improved for the printed circuit board. These boards are used in an appropriate device such as a computer. The component packing density requires high connection density. Hence, connection density has fairly severe demands, such that problems have been encountered by the mere placement of the connector on an edge of a printed circuit board. For example, connectors have to be spaced at a spacing of about 0.050 inches center line to center line. These spacings have not been sufficient, and further density of these contacts has been obtained by placing two rows of contacts in line, one over the other, each making a connection to a different printed circuit board lead or pad; a contact lead width of less than 0.020 has been used for the above 0.050 center line to center line connectors.
Accordingly, the pads on the circuit board have been on the same 0.050 centerline as the connector contacts, and these very slim, reed-like contacts have had to be very carefully aligned so that these could he properly connected to the pads on the printed circuit board and thus readied for reflow soldering.
Various attempts have been made to assure contact integrity, but great difficulties have arisen by the mere mechanical placement of the connector contacts on the printed circuit boards. These rather fragile and easily distortable contacts have tended to be easily damaged, and although various aids have been used such as plastic insertion sheets to help avoid damage, the individual contacts have still been misplaced and/or have warped during reflow soldering. Further, there has been no satisfactory way of increasing the density of these contacts because of the high density connection requirements for modern circuit boards. While a number of attempts have been made to assure proper placement of the connector contacts after the placement of the connector has been achieved, the proper alignment has often been wanting and a number of reliability problems have appeared. These reliability problems are especially severe when one considers the loss associated by just one cotact not functioning and this one contact being the result of misalignment of just one of the connector contacts with the printed circuit board. Consequently, contact integrity and reliability are severe problems in the assembly of circuit boards for which a series of solutions have been offered, none of which has been satisfactory.